This invention concerns a liquid processing composition for silver complex diffusion transfer process.
The silver complex diffusion transfer process (referred to as "DTR process" hereinafter) is well known and is disclosed in U.S. Pat. No. 2,352,014 and other patents and literatures. That is, in the DTR process, a silver complex is transferred imagewise by diffusion from the silver halide emulsion layer to the image receiving layer, where it is converted into a silver image generally in the presence of physical development nuclei. For this purpose, the silver halide emulsion layer exposed imagewise is placed or brought into contact with the image receiving layer in the presence of a developing agent and a silver halide solvent to convert the undeveloped silver halides to a soluble silver complex. The silver halide in the exposed portion of the silver halide emulsion layer is reduced to silver which, therefore, can no longer be dissolved and diffused. On the other hand, the silver halide in the unexposed portions of the silver halide emulsion layer is converted into a soluble silver complex, which is transferred to the image receiving layer where a silver image is formed generally in the presence of physical development nuclei.
Action of the silver halide in the exposed portions and that of the silver halide in the unexposed portions reverse in the case of fogged silver halide emulsions for direct positive.
DTR process can be widely employed for reproduction of documents, production of lithographic printing plates, production of block copies for plate making and for instant photography and the like.
Especially, in reproduction of documents and production of block copies for plate making, a negative material bearing a silver halide emulsion layer and a positive material bearing an image receiving layer containing physical development nuclei are allowed to contact with each other generally in a DTR processing solution containing a silver complex forming agent to form a silver image in the image receiving layer of the positive material. This silver image must be pure black or bluish black and must have sufficiently high density. Furthermore, high contrast and sharpness are required. In addition, high transfer speed is desirable.
Proposals for obtaining black silver images have been made in British Pat. No. 561875, Belgian Pat. No. 502525, Japanese Patent Examined Publications (Kokoku) No. 15734/64, No. 17747/64, No. 3957/65, No. 45542/72 and No. 1327/73 and Japanese Patent Unexamined Publication (Kokai) No. 49436/73, etc. Moreover, Japanese Patent Unexamined Publications (Kokai) No. 49436/73 and No. 1223/74 and Japanese Patent Examined Publications (Kokoku) No. 8146/64 and No. 25142/76 disclose improvement of density of silver images and Japanese Patent Examined Publication (Kokoku) No. 11093/63, No. 27568/64, No. 43778/76, etc. disclose improvement of transfer speed.
These specifications also describe contrast or sharpness of silver images formed on a positive material. Further consideration must be given on discoloration of white portions of positive materials as disclosed in Japanese Patent Examined Publications (Kokoku) No. 7296/63 and No. 17070/69 and on separability of negative material and positive material as disclosed in Japanese Patent Examined Publications No. 18134/63 and No. 15587/65.
However, the techniques proposed before do not satisfy all requirements, but have adverse effect on at least one other requirement. Therefore, all of the requirements cannot be easily satisfied even by combination of the known techniques and there has been a continuing need for overcoming the problems.
During developing process of silver halide photographic light sensitive materials, there are formed colored sludges in the developing solution which not only stain the solution, but stick to the photographic light sensitive materials and processing devices. Therefore, the developing solution must be often renewed or filtered. The silver halide in the films or printing papers is dissolved and enters the developing solution where it is reduced with developers to colloidal silver which is colored. Thus, the colored sludges are formed. A part of them easily coagulate and settle, but most of them float in the solution in the form of flocculated blackish brown dirty mud. Most of the developing solutions contain substances such as sodium sulfite which dissolve silver halides and so they have the defect as mentioned above. This defect is conspicuous in such developing solutions as for silver complex diffusion transfer process which contain water-soluble silver complex forming agents such as thiosulfates, thiocyanates, ammonia, ethanolamine and the like. The formation of the colored sludges can be retarded by lowering the temperature of the developing solution, but in this case the development is also delayed and so this is neither practical nor satisfactory.
Hitherto, it has been known that several mercapto heterocyclic compounds such as 1-phenyl-5-mercaptotetrazole and 2-thiazolidine-4-caboxylic acid and 4-acylamino-1,2,4-triazoline-5-thion which is disclosed in Japanese Patent Examined Publication (Kokoku) No. 26777/73 prevent the formation of the colored sludges. It is considered that these mercapto heterocyclic compounds form stable salts with silver halides dissolved in the developing solutions to prevent reduction to colloidal silver. However, these compounds have some unallowable defects, namely, when the processing solutions after used in development is left for several days the colored sludges are formed in a great amount; when the amount of these compounds added is increased to increase the effect of preventing the formation of the colored sludges, the developing speed is extremely decreased; or these compounds have only small effect of preventing the formation of the colored sludges.